Are our crocodiles on the move?

THE Gladstone region's spate of salt water crocodile sightings in recent weeks prompts the question - can we expect to see more crocodiles in Gladstone in the future? Are they getting more common because of climate change?

It depends on what time-frame you look at, says emeritus professor of zoology at the University of Queensland, Gordon Grigg.

Professor Grigg has been working with crocodiles on and off since the 1970s. When he retired in 2007, he spent seven years writing a comprehensive reference book - The Biology and Evolution of Crocodylians.

So you could say he knows a thing or two about crocs, and in the short term, he sees no reason to worry just yet about climate change causing an increase in crocodile numbers at the edge of their range.

"There's a tendency for people to think more animals have been seen south of Gladstone. There's a tendency for people to say they are becoming more common," he said.

"(But) people who are saying that also need to take into account that there are a lot more people out in boats than (there were) 30 to 40 years ago. There's a lot more people to observe them."

Professor Grigg says there's frequent stories about crocs moving south because of climate change but, he says, "it's premature to think climate change has got anything to do with seeing crocodiles down around the Sunshine Coast or Fraser Island".

He points out that crocodiles have been seen on and off much further south than Rockhampton for well over 100 years.

"One famous example is a 3.8-metre animal shot in the Logan River, south of Brisbane, in 1905. There's no doubt it got there under its own steam," he said.

Professor Grigg says that's one of the things with crocs, some of them like to roam.

He says satellite tracking data collected on the reptiles in Australia has found they are "surprisingly mobile".

"They can travel 20 kilometres a day without difficulty, they can also use water currents to assist them," he said.

"One crocodile was tracked down the west coast of Cape York, I think it went 600 kilometres, then it went back to where it was."

Professor Grigg says they are distributed right across to the Solomon Islands, which indicates they are able to traverse large stretches of open water.

"A related species in Belize (in the Carribbean), the crocs there go out and forage on the reef, eat fish and crabs, even though there's no land there for them, so our crocs have possibly got the capacity to do that as well," he said.

He said we already know "they go to and from islands in the northern part of the Gulf of Carpentaria to feed on hatchling√ turtles and to islands 80 km off the Kimberly Coast to sea bird rookeries".

When people spot them off the coast, "they are commonly travelling between rivers, the satellite tracking has shown they do a lot of coastal travel, they are seen on the Great Barrier Reef sometimes".

Scientists say the natural range of the crocodile ends at the Boyne River just south of Gladstone.

The reason for this, says Professor Grigg is probably crocodiles' dependence on warm weather to breed; once the eggs are laid in the nest, they are at the mercy of the weather.

Last week a crocodile was reported by an outrigger at Seventeen Seventy, the area is "atypical" for the reptiles.